Press for hydrostatic extrusion having a composite cylinder externally excused to high pressure

ABSTRACT

A press for hydrostatic extrusion includes a press stand and a high-pressure cylinder arranged in the press stand. These parts form a pressure chamber to enclose a pressure medium, and a piston is provided extending into the chamber for effecting a pressure in the enclosed pressure medium. A tubular element having a die at its inner end projects into the pressure chamber on the opposite end from the piston. The tubular element is formed of a number of tubes arranged one inside the other between which is an annular gap when the tubular element is unloaded; but the tubes come into contact when the outer part is subjected to working pressure.

Muted States Patent 1151 aesmn Lundstrom Web. 8, W72

[54] PRESS Mm HYDRQSTATH v [56] References (Titled EXTRUSKUN HAVING ACUMHUSHTE UNITED STATES PATENTS CYLINDER EXTERNALLY EXCUSEH 3,354,68511/1967 Green ..72/60 TO HIGH PRESSURE Hans Lundstrom, Robertsfors,Sweden Allrnanna Svenslra Eleldrislta Aktielmloget, Vasteras, SwedenFeb. 16, 1970 Inventor:

Assignee:

Filed:

Appl. No.:

Foreign Application Priority Data Primary EiaminerRichard J. HerbstAttorney1ennings Bailey, Jr.

Feb. 14, 1969 Sweden ..2024/69 U.S. Cl ..72/60, 72/271, 72/273 Int. Cl.B216 27/00 Field of Search ..72/60, 253, 271, 273

[ ABSTRACT I A press for hydrostatic extrusion includes a press standand a hi 'gh pressure cylinder arranged in the press stand. These partsform a pressure chamber to enclose a pressure medium, and a 5 Claims,Drawing Figures PATENTED FEB 8|87Z 3,640,111

sum 2 OF 3 INVENIOR. HAN 6 L \JN D317? 0 PATENTEUFEB em:

SHEET 3 OF 3 1 mass iron nvnnosrarrc EXTRUSKON KIAVHNGA COMPOSITECYLINDER EXTERNALLY EXCUSED TO I HIGH PRESSURE BACKGROUND OF THEINVENTION 1. Field of the Invention The present invention relates to apress for hydrostatic extrusion having a tubular member externallyexposed to a high pressure.

2. The Prior Art In presses for hydrostatic extrusion the length of thepressure-generating punch is limited by the buckling strength.

Thus the volume which can be pressed in one operating cycle is alsolimited. In order to be able to increase the billet length which can beextruded with a certain maximum punch length,

presses have in certain cases been designed in such a way that,

face of a tube which is subjected to an external overpressure is atleast twice as great as the external overpressure. According to theelasticity theory:

1- F y where o the tangential stress for a simple tube p the externalpressure r, inner radius r, outer radius At an external overpressure ofkilobar the tangential stress is at least 600 kg./mm. at the innersurface of the tube if it is not plastically deformed at the innersurface previously. if it is plastically deformed, tensile stressesoccur upon decompression which, with the hard material which mustnormally be used, cause cracking at the inner surface, and graduallyrupture.

SUMMARY OF THE INVENTION By means of the invention, hollow cylinderssuitable for die supports and the like can be manufactured, in whichlower tangential stress is obtained at the inner surface than whensupport it is usually constructed so that its outer tube takes up theaxial forces operating on the die.

In the embodiment according to the invention the tangential stress atthe inner surface of the cylinder is considerably reduced. If the axialstress in the cylinder is assumed to be zero, with a construction havingtwo tubes, one inside the other and a suitable gap between the tubes,the condition being fulfilled that the equivalent tensile stress at theinner edge of both tubes is equal and as small as possible, and that theratio between the thickness of the material in the tubes is optimallyselected, the maximum tangential pressure stress at the inner radius ofthe tubes will be where r the outer radius of the composite cylinder Theadvantage of a double-walled cylinder in comparison with a single-walledcylinder is clear from the following table:

where o is the tangential stress of the inner radius of a singlewalledcylinder.

,It is possible to use more than two tubes and thus further reduce themaximum tangential pressure stress.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is further describedwith reference to the accompanying drawings.

FIG. 1 shows schematically a press for hydrostatic extrusion where thedie support is used as a punch which can be inserted into a pressurechamber.

FIG. 2 shows on a larger scale the die support itself.

FIG. 3 shows a press having a pressure-multiplier.

1 FIG. 4 shows a detail of an ordinary extrusion press having a diesupport according to the invention.

FIG. 5 shows an embodiment in which the die itself and the die supportform an integrated unit.

' DESCRIPTION OF THE PREFERRED EMBODIMENTS In the drawings 1 designatesa press piston and 2 a press table on a horizontal hydraulic press, nototherwise shown. The press comprises a pressure-generating punch 3 whichis firmly attached to the piston I by means of a clamping ring 4 and astationary punch 5 which is attached to the press table 2 by means of aclamping ring 6. The punch 5 forms a support for a die 7. The pressurecylinder 8 is axially displaceable and is forced in over the stationarypunch 5 of the piston I when the punch 3 has been completely inserted inthe cylinder 8.

. The part of the punch 5 which is inside the seal 9 will be subjectedto an external overpressure by the pressure medium enclosed in thecylinder. In order to be able to withstand the high pressure the punchaccording to the invention consists of two concentric tubes 10 and '11between which at the innermost part of the punch is a seal 12 whichprevents pressure medium from penetrating between the tubes. The outerdiameter of the tube 11 is smaller than the inner diameter of the tube10 so that-a'gap I3 exists between the tubes when the punch is not (rthe tangential stress for a cylinder constructed of two loaded. The tubeIll is somewhat shorter than the tube 10 and it will therefore take upall the axial force operating on the die 7 during the compression.

1 In FIG. 3, 21 designates a pressure-generating punch and 22 a presstable in a press not otherwise shown. The compression equipment isintended for hydrostatic extrusion at ultrahigh pressure, by which ismeant pressures in the order of magnitude of 25 kilobar or more. On thepress table 22 rests a high-pressure cylinder, usually the typecomprising an inner tube 23 surrounded by a prestressed strip sheath 24.The punch 21 projects into the tube 23 of the cylinder and generates apressure in a pressure medium enclosed in the cylinder space 25. In thecylinder is a unit consisting of a pressure multiplier and a pressurechamber 27. The pressure multiplier 26 comprises a differential piston28 which is axially movable in a chamber with a space 29 filled with gasunder low pressure or partly or entirely evacuated. In accordance withthe invention, this is formed of two concentric tubes 39 and 31 betweenwhich is a gap 32 when the chamber is not loaded. At the upper and lowerparts of the chamber are rings 33 and 34. Between the ring 33 and thepiston 28 is a sealing ring 35. The pressure chamber 27 consists of aninner tube 36 and an outer prestressed tube 37. In the pressure chamberis a die 38 and also a billet 39. The space 40 is filled with a pressuremedium which hydrostatically presses against the billet 39. The entireunit of pressure multiplier 26 and pressure chamber 27 is surrounded bya tube M which is connected to the ring 33 by a weld 42. Between thepressure chamber tube 23 and the sealing tube 41 is a sealing ring 43and a support ring 44 for the sealing ring. Between the die 38 and thetube 36 is a sealing ring and between the piston 28 and the cylinder 36is a sealing ring 45.

The space 29 for the pressure multiplier is sealed from the space 25filled with pressure medium in the outer pressure chamber by the tube 41and the piston 28 with the seal 35. It is also sealed from the space 40in the enclosed pressure chamber 27 by the lower part of the piston 28with the seal 45.

During the extrusion the piston 21 is pressed into the. space 25 of thehigh-pressure chamber and generates a pressure which externallyinfluences the pressure multiplier 26 which is constructed in accordancewith the invention with tubes 30 and 31 between which is a gap 32 whenthe pressure of the presing into the high-pressure cylinder, and aguide54. Between the high-pressure cylinder 51 and the part 53 is agasket 55.

In the embodiment according to FIG. 4 a die 56 rests on a die supportconsisting of an outer short tube or ring 57 and an inner tube or ring58. Between these is a gap 59 when the pressure in the space 60 is low.This gap disappears when the pressure increases so that the ring 57 iscompressed and its diameter decreases. At high pressure it will then besupported by the ring 58. The joint between the die 56 and the ring 57is covered by a sleeve 61 of elastomeric material which preventspressure medium in the space 60 from penetrating between the die 56 andthe ring 57. Between the ring 57 and'the part 53 of the disc 52 is aseal 62 which prevents pressure medium from passing between the diesupport and the part 53. The guide 54 centers the die support withrespect to the opening 63 in the plate 52. Because of the structureshown, the distance between the extrusion edge 64 and the base surfaceof the die 56 can be kept very short, thus preventing the materialaround the hole in the die under the extrusion edge from beingplastically deformed during the extrusion. This plastic deformationwould result in a tangential tensile stress upon decompression whichmight give rise to radial cracks along the extrusion edge 64, the diebeing thus damaged.

In the embodiment according to FIG. 5, the die and die support are anintegrated unit. The die 70 is externally conical at its lower part andsurrounded at this part by an internally conical ring 71. The coneangles of the die 70 and the ring 71 are selected so that at least inthe area under the extrusion edge 64 a gap 73 is formed.

I claim:

1. A press for hydraulic extrusion comprising a press stand, ahighpressure cylinder part arranged in the press stand, a tubularelement extending into the interior of the high-pressure cylinder andspaced inwardly from the wall thereof, at least a part of said tubularelement comprising at least inner and outer tubes arranged one insidethe other having an annular space therebetween and means sealing theannular space from the interior of the high-pressure cylinder, and meansto produce in the high-pressure cylinder on the outside of the outertube a pressure substantially greater than the pressure existing betweenthe tubes, whereby contact between the tubes is caused when the outertube is subjected to pressure above a predetermined amount.

2. Press according to claim 1, in which the tubular element comprises apressure-amplifier (26).

3. Press according to claim 1, having an extrusion die, the tubularelement (5) forming a support for the extrusion die (7) and taking upaxial forces operating on the die.

4. Press according to claim 1, in which the inner part of the tubularelement comprises a die 5. Press according to claim 1, in which thetubular element is composed of conical tube parts (70, 71

1. A press for hydraulic extrusion comprising a press stand, a high-pressure cylinder part arranged in the press stand, a tubular element extending into the interior of the high-pressure cylinder and spaced inwardly from the wall thereof, at least a part of said tubular element comprising at least inner and outer tubes arranged one inside the other having an annular space therebetween and means sealing the annular space from the interior of the high-pressure cylinder, and means to produce in the high-pressure cylinder on the outside of the outer tube a pressure substantially greater than the pressure existing between the tubes, whereby contact between the tubes is caused when the outer tube is subjected to pressure above a predetermined amount.
 2. Press according to claim 1, in which the tubular element comprises a pressure-amplifier (26).
 3. Press according to claim 1, having an extrusion die, the tubular element (5) forming a support for the extrusion die (7) and taking up axial forces operating on the die.
 4. Press according to claim 1, in which the inner part of the tubular element comprises a die (70).
 5. Press according to claim 1, in which the tubular element is composed of conical tube parts (70, 71). 